(1) Field of the Invention
The invention relates to a two-phase asynchronous motor device for driving systems for closing a building, of the roller shutter type.
The present invention relates to the field of the systems for closing a building and in particular to roller shutters and their motorization.
(2) Description of the Prior Art
Many motorized systems for closing a building, which are in addition associated with remote-control devices facilitating the control of their opening and closing, are already known.
In the particular field of the roller shutters, the driving motor is of the tubular type, so as to be positioned inside the winding-up tube onto which the apron of the roller shutter is designed capable of winding up.
This is usually an asynchronous motor with a phase-shift capacitor including a main winding and a secondary winding allowing not only reversing the direction of rotation of the motor, but in addition, through the phase shift of the current generated by the capacitor, generating a driving torque at the level of the rotor of this motor. The secondary winding is preferably different from the main winding in that it has a different resistance and inductance and thus facilitates the starting of the motor.
Because of manufacturing constraints, some manufacturers design imperfect single-phase motors with a secondary winding, which is identical to the main winding. This obliges them to use a larger capacitor, which gets hotter. Obviously, the encapsulation of such a motor in a casing made out of synthetic insulating material and its installation inside a winding-up tube of a roller shutter do not facilitate the evacuation of the calories produced.
Turning back to the operation of this type of motor, the stator currents create a rotary magnetic field in the stator, while the rotor is comprised of short-circuited leads through which pass currents induced by the stator magnetic field.
The starting torque of such an asynchronous motor with a capacitor depends on the value of the latter. Anyway, this type of motor operates optimally, under nominal current-supply conditions, only beyond a determined speed of rotation.
This being said, within the framework of their application to roller shutters, it should be noted that, though nearly no power is required for unwinding an apron of such a roller shutter and that a lower starting torque is enough, since only the inertia during the rotation of the winding-up tube of the apron has to be overcome, the problem is different during the winding-up.
Of course, when the apron of the roller shutter is fully unfolded and the openings between the hinged slats forming said apron are closed, the load to be driven by the motor during the first turns of rotation is lesser and the torque to be produced is itself reduced. However, when this roller-shutter apron is in a partially, even nearly fully unfolded situation, without the openings between the slats being closed, the control to wind up the roller shutter results, under such circumstances, into heavily loading the motor. In this case, this motor should be capable of producing a high starting torque in order to overcome the reverse torque the weight of the apron exerts onto the winding-up tube.
It is therefore usual, in this field of application of the roller shutters, to use motors with a nominal power much higher than the power that is normally required.
Though this results into an extra cost, it also results into the usefulness of making use of a plurality of motors with different powers to cover the full range of roller shutters one wants to motorize.
In addition, the extra power of the motor, which is finally useful only during the starting phase, i.e. during a transient phase in which the motor does not operate in an optimal way, results into heavily loading the mechanical elements of the roller shutter, whether in the event of an unexpected blocking or in the event of a control to stop the operation.
It is in particular usual to ensure the stoppage of the motor, at the travel end for unwinding or winding-up the apron of the roller shutter, for example through measuring the phase shift between current and voltage. This phase shift results from an increase of the load applied to the motor, which results, in this case, from the arrival at the lower of upper travel end of the apron. Under such circumstances, one understands very well that, before the interruption of the current supply to the motor occurs, the latter exerts an excessive strain on the mechanical elements of the roller shutter, due to its overdimensioning.
It should also be noted that this type of motor is usually provided with an electromagnetic brake operating in the absence of current. Of course, the higher the power of the motor, the more this brake is loaded and must be oversized accordingly.
Besides this low starting torque produced by an asynchronous motor with main and secondary windings, this under nominal current-supply conditions, in this case a nominal voltage of 230 Volts and a frequency of 50 Hertz, there is also the problem of the network-voltage variation. In other words, this voltage of the current-supply network of a dwelling is not constant and equal to the nominal value of 230 Volts, but can vary. In particular, it can be lower than this nominal voltage and, in such a case, the starting torque such an asynchronous motor is likely to produce has a tendency to quickly decrease.
In particular, it could be noted that below a voltage of 180 Volts the motor is often unable to start. Therefore, this variable of the supply voltage of the motor should also be taken into consideration for the dimensioning of the latter.
Finally, if one takes into consideration all the strains the motorization of a roller shutter represents, one must necessarily conclude that a three-phase motor should be used.
Furthermore, as soon as one wants a motor with certain performances or one wants to meet particular constraints, a balanced three-phase motor is systematically used, which a power converter in the form of a speed-varying device is usually associated with, so that all these requirements can be met.
However, for such an application of a three-phase motor with speed variation to a roller shutter, the specialist in the art can only observe that he is facing an unavoidable or nearly unavoidable requirement, namely the maximum cross-section the tubular motor can adopt for its accommodation in the winding-up tube of the roller shutter.
The three-phase motor has indeed too large a cross-section to allow such an installation. Of course, it can be contemplated to increase this cross-section of the winding-up tube, but this results into a larger cross-section of the roller-shutter apron when wound up, thus of the box in which this roller-shutter mechanism unit is accommodated, in addition to the fact that the implications at the level of such a building for the latter to be able of receiving such oversized boxes. For example, their installation in the thickness of a wall can be made impossible. An installation against the inner side of a building causes this voluminous box to be more protruding into the dwelling. In the event of a renewal, a thicker box reduces accordingly the surface for the passing through of light at the level of a window. This is completely contrary to the current tendency consisting in making the box of a roller shutter as discrete as possible and in facilitating its integration into a building.
Another solution consists in placing such a three-phase motor at an end of said winding-up tube, instead of integrating it into the latter. This also results into a lateral extension of the box of the roller shutter corresponding to the additional size created by this motor, which of course results into specific arrangements to be foreseen at the level of the building.
As can be observed, the three-phase motor, though it is perfectly adapted for driving a roller-shutter apron, could not be used in this field of application, because of unavoidable dimensional constraints.
Therefore, the specialist in the art has systematically turned towards the only motor he thought capable of technically and economically solving the problems of the motorized driving of the roller shutters, namely the single-phase asynchronous motor with a capacitor.